Does she speak German fluently? If not, German Kindergarten may be enough of a challenge as long as you tell them not to speak English to your daughter. My son is 3 and goes to a German Kindergarten in Hoheinod (South of Landstuhl) and he only really goes to learn German and socialize. As far as learning other things, we've had to take it into our own hands. He can write the entire Alphabet and numbers 0-9. Just two days ago he started learning to read in English. He's been quite successful. Start with a bunch of books, then pads of paper for practicing letter, then on to a dry-erase board as a reward for doing so well on paper. That's how we kept learning fun. Currently we have a reward system that keeps him trying with the reading which is every day that he tries for an hour to read he gets one chocolate, once he can read a 1st Stage begining reader book he gets to pick out a toy at Toys R US. I've also challenged my son by doing mini-Science projects like volcanos and observing insects and using my old College Biology book to identify all the different parts on a flower, which I quiz him on through out the week.
As for me: I am a SAHM with a 3 year old son and a 2 month old daughter, we haven't decided how long we'll be here in Germany with the military yet... but we hope to be in Germany for quite some time.